Chapter IV Process Failure Mode and Effects Analysis 94 Action Results Actions Taken Completion Date Responsibility & Target Completion Date Recommended Action Potential Cause(s) of Failure Potential Effect(s) of Failure Potential Failure Mode Requirement Function Prevention Detection Detection Detection Occurrence Occurrence Severity Severity Classification Controls Controls RPN RPN POTENTIAL FAILUREMODEAND EFFECTSANALYSIS (PROCESSFMEA) Process Responsibility ______________________________________ Key Date __________________________________________________ Item: _________________________________________________ Model Core Team Current Process FMEA Number f o egaPPrepared By: FMEA Date (Orig.) Process Step Year(s)/Program(s)_________________________________ Deteriorated life of door leading to: • • Unsatisfactory appearance due to rust through paint over time. Impaired function of interior door hardware Corroded interior lower door panels 7 Allows integrity breach of inner door panel Op 70: Manual application of wax inside door panel Cover inner door, lower surfaces with wax to specification thickness Insufficient wax coverage over specified surface Excessive wax coverage over specified surface Stop added, sprayer checked online Add positive depth stop to sprayer Mfg Engineering by 0X 10 15 Variables check for film thickness Visual check for coverage. Variables check for film thickness Visual check for coverage. Variables check for film thickness Visual check for coverage. None Manually inserted spray head not inserted far enough Temp and Press Limits were determined and limit controls have been installed- Control charts show process is in control Cpk=1.85 Use Design of experiments (DOE) on viscosity vs. temperature vs. pressure Mfg Engineering by0X 10 01 Test spray at start-up and after idle periods and preventative maintenance program to clean heads Spray head clogged - Viscosity too high - Temperature too low- Pressure too low 8 5 5 5 280 175 7035 725 715 None Preventative maintenance programs to maintain heads Spray head deformed due to impact 25 75 70 245 Automatic spray timer installed- operator starts spray, timer controls shut-off control charts show process is in control – Cpk=2.05 Install Spray timer. Maintenance XX/XX/XX Operator instructions Lot sampling (visual) check coverage of critical areas None Spray time sufficient 49 717 Automate spraying Mfg Engineering by 0X 12 15 Rejected due to complexity of different doors on the same line SAMPLE a2 c d e f g h i j k m ----n---- l h b 1a B D G A F C E H Table IV.1 Sample PFMEA Form with Minimal Information Elements & Example Entries
Chapter IV Process Failure Mode and Effects Analysis 95 Current Process Controls (h) Current Process Controls are descriptions of the controls that can either prevent to the extent possible, the cause of failure from occurring or detect the failure mode or cause of failure should it occur. There are two types of Process Controls to consider: Prevention: Eliminate (prevent) the cause of the failure or the failure mode from occurring, or reduce its rate of occurrence. Detection: Identify (detect) the cause of failure or the failure mode, leading to the development of associated corrective action(s) or countermeasures. The preferred approach is to first use prevention controls, if possible. The initial occurrence rankings will be affected by the prevention controls provided they are integrated as part of the process. The initial detection rankings will be based on process controls that either detect the cause of failure, or detect the failure mode. Because statistical charting methods (i.e., Statistical Process Control)11 typically use sampling to assess process stability and detect out-of-control conditions they should not be considered when evaluating the effectiveness of specific Detection Controls. SPC may, however, be considered as a Prevention Control for specific causes whose trends are identifiable in advance of an actual non-conformance being produced, such as tool wear. The example PFMEA form in this manual has two separate columns for Prevention Controls and Detection Controls to assist the team in clearly distinguishing between these two types of controls. This allows for a quick visual determination that both types of process controls have been considered. If a one-column (for process controls) form is used, then the following prefixes should be used. For prevention controls, place a 'P' before or after each prevention control listed. For detection controls, place a 'D' before or after each detection control listed (see Table IV.4 Example of Causes and Controls). 11 See Chrysler, Ford, GM; SPC Manual, AIAG.
Chapter IV Process Failure Mode and Effects Analysis 96 Requirement Failure Mode Cause Prevention Control Detection Control Screws torqued until fully seated Screw not fully seated Nut runner not held perpendicular to work surface by operator Operator training Angle sensor included in nut runner to detect cross-threading not allowing part to be removed from fixture until value is satisfied Torque setting set too high by nonset-up personnel Password protected control panel (only set-up personnel have access) Torque validation box included in set-up procedure to validate setting prior to running Training of set-up personnel Torque validation box included in set-up procedure to validate setting prior to running Screw torqued too high Torque setting set too high by set-up personnel Settings added to set-up instructions Torque setting set too low by nonset-up personnel Password protected control panel (only set-up personnel have access) Torque validation box included in set-up procedure to validate setting prior to running Training of set-up personnel Torque validation box included in set-up procedure to validate setting prior to running Screws torqued to dynamic torque specification Screw torqued too low Torque setting set too low by set-up personnel Settings added to set-up instructions Table IV.4 Examples of Causes and Controls
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Chapter IV Process Failure Mode and Effects Analysis 98 Action Results Actions Taken Completion Date Responsibility & Target Completion Date Recommended Action Potential Cause(s) of Failure Potential Effect(s) of Failure Potential Failure Mode Requirement Function Prevention Detection Detection Detection Occurrence Occurrence Severity Severity Classification Controls Controls RPN RPN POTENTIAL FAILUREMODEAND EFFECTSANALYSIS (PROCESSFMEA) Process Responsibility ______________________________________ Key Date __________________________________________________ Item: _________________________________________________ Model Core Team Current Process FMEA Number f o egaPPrepared By: FMEA Date (Orig.) Process Step Year(s)/Program(s)_________________________________ Deteriorated life of door leading to: • • Unsatisfactory appearance due to rust through paint over time. Impaired function of interior door hardware Corroded interior lower door panels 7 Allows integrity breach of inner door panel Op 70: Manual application of wax inside door panel Cover inner door, lower surfaces with wax to specification thickness Insufficient wax coverage over specified surface Excessive wax coverage over specified surface Stop added, sprayer checked online Add positive depth stop to sprayer Mfg Engineering by 0X 10 15 Variables check for film thickness Visual check for coverage. Variables check for film thickness Visual check for coverage. Variables check for film thickness Visual check for coverage. None Manually inserted spray head not inserted far enough Temp and Press Limits were determined and limit controls have been installed- Control charts show process is in control Cpk=1.85 Use Design of experiments (DOE) on viscosity vs. temperature vs. pressure Mfg Engineering by0X 10 01 Test spray at start-up and after idle periods and preventative maintenance program to clean heads Spray head clogged - Viscosity too high - Temperature too low- Pressure too low 8 5 5 5 280 175 7035 725 715 None Preventative maintenance programs to maintain heads Spray head deformed due to impact 25 75 70 245 Automatic spray timer installed- operator starts spray, timer controls shut-off control charts show process is in control – Cpk=2.05 Install Spray timer. Maintenance XX/XX/XX Operator instructions Lot sampling (visual) check coverage of critical areas None Spray time sufficient 49 717 Automate spraying Mfg Engineering by 0X 12 15 Rejected due to complexity of different doors on the same line SAMPLE a2 c d e f g h i j k m ----n---- l h b 1a B D G A F C E H Table IV.1 Sample PFMEA Form with Minimal Information Elements & Example Entries
Chapter IV Process Failure Mode and Effects Analysis 99 Detection (D) (i) Detection is the rank associated with the best detection control listed in the Detection Controls column. Detection is a relative ranking within the scope of the individual FMEA. In order to achieve a lower ranking, generally the planned detection control has to be improved. When more than one control is identified, it is recommended that the detection ranking of each control be included as part of the description of the control. Record the lowest ranking value in the Detection column. Assume the failure has occurred and then assess the capabilities of all "Current Process Controls" to prevent shipment of the part having this failure mode. Do not automatically presume that the detection ranking is low because the occurrence is low, but do assess the ability of the process controls to detect low frequency failure modes or prevent them from going further in the process. Random quality checks are unlikely to detect the existence of an isolated problem and should not influence the detection ranking. Suggested Evaluation Criteria The team should agree on evaluation criteria and a ranking system and apply them consistently, even if modified for individual product analysis. Detection should be estimated using Table Cr3 as a guideline. The ranking value of one (1) is reserved for failure prevention through proven process design solutions.
Chapter IV Process Failure Mode and Effects Analysis 100 Opportunity for Detection Criteria: Likelihood of Detection by Process Control Rank Likelihood of Detection No detection opportunity No current process control; Cannot detect or is not analyzed. 10 Almost Impossible Not likely to detect at any stage Failure Mode and/or Error (Cause) is not easily detected (e.g., random audits). 9 Very Remote Problem Detection Post Processing Failure Mode detection post-processing by operator through visual/tactile/audible means. 8 Remote Problem Detection at Source Failure Mode detection in-station by operator through visual/tactile/audible means or post-processing through use of attribute gauging (go/no-go, manual torque check/clicker wrench, etc.). 7 Very Low Problem Detection Post Processing Failure Mode detection post-processing by operator through use of variable gauging or in-station by operator through use of attribute gauging (go/no-go, manual torque check/clicker wrench, etc). 6 Low Problem Detection at Source Failure Mode or Error (Cause) detection in-station by operator through use of variable gauging or by automated controls in-station that will detect discrepant part and notify operator (light, buzzer, etc.). Gauging performed on setup and first-piece check (for set-up causes only). 5 Moderate Problem Detection Post Processing Failure Mode detection post-processing by automated controls that will detect discrepant part and lock part to prevent further processing. 4 Moderately High Problem Detection at Source Failure Mode detection in-station by automated controls that will detect discrepant part and automatically lock part in station to prevent further processing. 3 High Error Detection and/or Problem Prevention Error (Cause) detection in-station by automated controls that will detect error and prevent discrepant part from being made. 2 Very High Detection not applicable; Error Prevention Error (Cause) prevention as a result of fixture design, machine design or part design. Discrepant parts cannot be made because item has been error-proofed by process/product design. 1 Almost Certain Table Cr3 Suggested Process FMEA Detection Evaluation Criteria
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Chapter IV Process Failure Mode and Effects Analysis 102 Action Results Actions Taken Completion Date Responsibility & Target Completion Date Recommended Action Potential Cause(s) of Failure Potential Effect(s) of Failure Potential Failure Mode Requirement Function Prevention Detection Detection Detection Occurrence Occurrence Severity Severity Classification Controls Controls RPN RPN POTENTIAL FAILUREMODEAND EFFECTSANALYSIS (PROCESSFMEA) Process Responsibility ______________________________________ Key Date __________________________________________________ Item: _________________________________________________ Model Core Team Current Process FMEA Number f o egaPPrepared By: FMEA Date (Orig.) Process Step Year(s)/Program(s)_________________________________ Deteriorated life of door leading to: • • Unsatisfactory appearance due to rust through paint over time. Impaired function of interior door hardware Corroded interior lower door panels 7 Allows integrity breach of inner door panel Op 70: Manual application of wax inside door panel Cover inner door, lower surfaces with wax to specification thickness Insufficient wax coverage over specified surface Excessive wax coverage over specified surface Stop added, sprayer checked online Add positive depth stop to sprayer Mfg Engineering by 0X 10 15 Variables check for film thickness Visual check for coverage. Variables check for film thickness Visual check for coverage. Variables check for film thickness Visual check for coverage. None Manually inserted spray head not inserted far enough Temp and Press Limits were determined and limit controls have been installed- Control charts show process is in control Cpk=1.85 Use Design of experiments (DOE) on viscosity vs. temperature vs. pressure Mfg Engineering by0X 10 01 Test spray at start-up and after idle periods and preventative maintenance program to clean heads Spray head clogged - Viscosity too high - Temperature too low- Pressure too low 8 5 5 5 280 175 7035 725 715 None Preventative maintenance programs to maintain heads Spray head deformed due to impact 25 75 70 245 Automatic spray timer installed- operator starts spray, timer controls shut-off control charts show process is in control – Cpk=2.05 Install Spray timer. Maintenance XX/XX/XX Operator instructions Lot sampling (visual) check coverage of critical areas None Spray time sufficient 49 717 Automate spraying Mfg Engineering by 0X 12 15 Rejected due to complexity of different doors on the same line SAMPLE a2 c d e f g h i j k m ----n---- l h b 1a B D G A F C E H Table IV.1 Sample PFMEA Form with Minimal Information Elements & Example Entries
Chapter IV Process Failure Mode and Effects Analysis 103 Determining Action Priorities Once the team has completed the initial identification of failure modes and effects, causes and controls, including rankings for severity, occurrence and detection, they must decide if further efforts are needed to reduce the risk. Due to the inherent limitations on resources, time, technology, and other factors, they must choose how to best prioritize these efforts. The initial focus of the team should be oriented towards failure modes with the highest severity rankings. When the severity is 9 or 10, it is imperative that the team ensure that the risk is addressed through existing design controls or recommended actions (as documented in the FMEA). For failure modes with severities of 8 or below the team should consider causes having the highest occurrence or detection rankings. It is the team’s responsibility to look at the information, decide upon an approach, and determine how to best prioritize their risk reduction efforts which best serve their organization and customers. Risk Evaluation; Risk Priority Number (RPN) (j) One approach to assist in action prioritization has been to use the Risk Priority Number: RPN = Severity (S) x Occurrence (O) x Detection (D) Within the scope of the individual FMEA, this value can range between 1 and 1000. The use of an RPN threshold is NOT a recommended practice for determining the need for actions. Applying thresholds assumes that RPNs are a measure of relative risk (which they often are not) and that continuous improvement is not required (which it is). For example, if the customer applied an arbitrary threshold of 100 to the following, the supplier would be required to take action on the characteristic B with the RPN of 112. Item Severity Occurrence Detection RPN A 9 2 5 90 B 7 4 4 112 In this example, the RPN is higher for characteristic B than characteristic A. However, the priority should be to work on A with the higher severity of 9, although its RPN is 90 which is lower and below the threshold.
Chapter IV Process Failure Mode and Effects Analysis 104 Action Results Actions Taken Completion Date Responsibility & Target Completion Date Recommended Action Potential Cause(s) of Failure Potential Effect(s) of Failure Potential Failure Mode Requirement Function Prevention Detection Detection Detection Occurrence Occurrence Severity Severity Classification Controls Controls RPN RPN POTENTIAL FAILUREMODEAND EFFECTSANALYSIS (PROCESSFMEA) Process Responsibility ______________________________________ Key Date __________________________________________________ Item: _________________________________________________ Model Core Team Current Process FMEA Number f o egaPPrepared By: FMEA Date (Orig.) Process Step Year(s)/Program(s)_________________________________ Deteriorated life of door leading to: • • Unsatisfactory appearance due to rust through paint over time. Impaired function of interior door hardware Corroded interior lower door panels 7 Allows integrity breach of inner door panel Op 70: Manual application of wax inside door panel Cover inner door, lower surfaces with wax to specification thickness Insufficient wax coverage over specified surface Excessive wax coverage over specified surface Stop added, sprayer checked online Add positive depth stop to sprayer Mfg Engineering by 0X 10 15 Variables check for film thickness Visual check for coverage. Variables check for film thickness Visual check for coverage. Variables check for film thickness Visual check for coverage. None Manually inserted spray head not inserted far enough Temp and Press Limits were determined and limit controls have been installed- Control charts show process is in control Cpk=1.85 Use Design of experiments (DOE) on viscosity vs. temperature vs. pressure Mfg Engineering by0X 10 01 Test spray at start-up and after idle periods and preventative maintenance program to clean heads Spray head clogged - Viscosity too high - Temperature too low- Pressure too low 8 5 5 5 280 175 7035 725 715 None Preventative maintenance programs to maintain heads Spray head deformed due to impact 25 75 70 245 Automatic spray timer installed- operator starts spray, timer controls shut-off control charts show process is in control – Cpk=2.05 Install Spray timer. Maintenance XX/XX/XX Operator instructions Lot sampling (visual) check coverage of critical areas None Spray time sufficient 49 717 Automate spraying Mfg Engineering by 0X 12 15 Rejected due to complexity of different doors on the same line SAMPLE a2 c d e f g h i j k m ----n---- l h b 1a B D G A F C E H Table IV.1 Sample PFMEA Form with Minimal Information Elements & Example Entries
Chapter IV Process Failure Mode and Effects Analysis 105 Another concern with using the threshold approach is that there is no specific RPN value that requires mandatory action. Unfortunately, establishing such thresholds may promote the wrong behavior causing team members to spend time trying to justify a lower occurrence or detection ranking value to reduce the RPN. This type of behavior avoids addressing the real problem that underlies the cause of the failure mode and merely keeps the RPN below the threshold. It is important to recognize that while determining “acceptable” risk at a particular program milestone (e.g., vehicle launch) is desirable, it should be based on an analysis of severity, occurrence and detection and not through the application of RPN thresholds. Use of the RPN index in the discussions of the team can be a useful tool. The limitations of the use of RPN need to be understood. However, the use of RPN thresholds to determine action priority is not recommended. Recommended Action(s) (k) In general, prevention actions (i.e., reducing the occurrence) are preferable to detection actions. An example of this is the use of process design error proofing rather than random quality checks or associated inspection. The intent of any recommended action is to reduce rankings in the following order: severity, occurrence, and detection. Example approaches to reduce these are explained below: • To Reduce Severity (S) Ranking: Only a design or process revision can bring about a reduction in the severity ranking. A product/process design change, in and of itself, does not imply that the severity will be reduced. Any product/process design change should be reviewed by the team to determine the effect on the product functionality and process. For maximum effectiveness and efficiency of this approach, changes to the product and process design should be implemented early in the development process. For example, process technology needs to be considered very early in the process development if severity is to be reduced. • To Reduce Occurrence (O) Ranking: To reduce occurrence, process and design revisions may be required. A reduction in the occurrence ranking can be effected by removing or controlling one or more of the causes of the failure mode through a product or process design revision. Studies to understand the sources of variation of the process using statistical methods may be implemented. These studies
Chapter IV Process Failure Mode and Effects Analysis 106 Action Results Actions Taken Completion Date Responsibility & Target Completion Date Recommended Action Potential Cause(s) of Failure Potential Effect(s) of Failure Potential Failure Mode Requirement Function Prevention Detection Detection Detection Occurrence Occurrence Severity Severity Classification Controls Controls RPN RPN POTENTIAL FAILUREMODEAND EFFECTSANALYSIS (PROCESSFMEA) Process Responsibility ______________________________________ Key Date __________________________________________________ Item: _________________________________________________ Model Core Team Current Process FMEA Number f o egaPPrepared By: FMEA Date (Orig.) Process Step Year(s)/Program(s)_________________________________ Deteriorated life of door leading to: • • Unsatisfactory appearance due to rust through paint over time. Impaired function of interior door hardware Corroded interior lower door panels 7 Allows integrity breach of inner door panel Op 70: Manual application of wax inside door panel Cover inner door, lower surfaces with wax to specification thickness Insufficient wax coverage over specified surface Excessive wax coverage over specified surface Stop added, sprayer checked online Add positive depth stop to sprayer Mfg Engineering by 0X 10 15 Variables check for film thickness Visual check for coverage. Variables check for film thickness Visual check for coverage. Variables check for film thickness Visual check for coverage. None Manually inserted spray head not inserted far enough Temp and Press Limits were determined and limit controls have been installed- Control charts show process is in control Cpk=1.85 Use Design of experiments (DOE) on viscosity vs. temperature vs. pressure Mfg Engineering by0X 10 01 Test spray at start-up and after idle periods and preventative maintenance program to clean heads Spray head clogged - Viscosity too high - Temperature too low- Pressure too low 8 5 5 5 280 175 7035 725 715 None Preventative maintenance programs to maintain heads Spray head deformed due to impact 25 75 70 245 Automatic spray timer installed- operator starts spray, timer controls shut-off control charts show process is in control – Cpk=2.05 Install Spray timer. Maintenance XX/XX/XX Operator instructions Lot sampling (visual) check coverage of critical areas None Spray time sufficient 49 717 Automate spraying Mfg Engineering by 0X 12 15 Rejected due to complexity of different doors on the same line SAMPLE a2 c d e f g h i j k m ----n---- l h b 1a B D G A F C E H Table IV.1 Sample PFMEA Form with Minimal Information Elements & Example Entries
Chapter IV Process Failure Mode and Effects Analysis 107 may result in actions that reduce occurrence. Further, the knowledge gained may assist in the identification of suitable controls including ongoing feedback of information to the appropriate operations for continuous improvement and problem prevention. • To Reduce Detection (D) Ranking: The preferred method is the use of error/mistake proofing. A redesign of the detection methodology may result in a reduction of the detection ranking. In some cases, a design change to a process step may be required to increase the likelihood of detection (i.e., reduce the detection ranking.) Generally, improving detection controls requires the knowledge and understanding of the dominant causes of process variation and any special causes. Increasing the frequency of inspection is usually not an effective action and should only be used as a temporary measure to collect additional information on the process so that permanent preventive/corrective action can be implemented12. If the assessment leads to no recommended actions for a specific failure mode/cause/control combination, indicate this by entering “None” in this column. It may be useful to also include a rationale if “None” is entered, especially in case of high severity. For process actions, the evaluation may include but is not limited to a review of: • Results of process DOE or other testing when applicable • Modified process flow diagram, floor plan, work instructions or preventive maintenance plan • Review of equipment, fixtures or machinery specifications • New or modified sensing/detection device Table IV.5 below provides an example of the application of causes (Column f), controls (Column h) and recommended actions (Column k). Responsibility & Target Completion Date (l) Enter the name of the individual and organization responsible for completing each recommended action including the target completion date. The process-responsible engineer/team leader is responsible for ensuring that all actions recommended have been implemented or adequately addressed. 12 See Chrysler, Ford, GM; SPC Manual, AIAG.
Chapter IV Process Failure Mode and Effects Analysis 108 Action Results Actions Taken Completion Date Responsibility & Target Completion Date Recommended Action Potential Cause(s) of Failure Potential Effect(s) of Failure Potential Failure Mode Requirement Function Prevention Detection Detection Detection Occurrence Occurrence Severity Severity Classification Controls Controls RPN RPN POTENTIAL FAILUREMODEAND EFFECTSANALYSIS (PROCESSFMEA) Process Responsibility ______________________________________ Key Date __________________________________________________ Item: _________________________________________________ Model Core Team Current Process FMEA Number f o egaPPrepared By: FMEA Date (Orig.) Process Step Year(s)/Program(s)_________________________________ Deteriorated life of door leading to: • • Unsatisfactory appearance due to rust through paint over time. Impaired function of interior door hardware Corroded interior lower door panels 7 Allows integrity breach of inner door panel Op 70: Manual application of wax inside door panel Cover inner door, lower surfaces with wax to specification thickness Insufficient wax coverage over specified surface Excessive wax coverage over specified surface Stop added, sprayer checked online Add positive depth stop to sprayer Mfg Engineering by 0X 10 15 Variables check for film thickness Visual check for coverage. Variables check for film thickness Visual check for coverage. Variables check for film thickness Visual check for coverage. None Manually inserted spray head not inserted far enough Temp and Press Limits were determined and limit controls have been installed- Control charts show process is in control Cpk=1.85 Use Design of experiments (DOE) on viscosity vs. temperature vs. pressure Mfg Engineering by0X 10 01 Test spray at start-up and after idle periods and preventative maintenance program to clean heads Spray head clogged - Viscosity too high - Temperature too low- Pressure too low 8 5 5 5 280 175 7035 725 715 None Preventative maintenance programs to maintain heads Spray head deformed due to impact 25 75 70 245 Automatic spray timer installed- operator starts spray, timer controls shut-off control charts show process is in control – Cpk=2.05 Install Spray timer. Maintenance XX/XX/XX Operator instructions Lot sampling (visual) check coverage of critical areas None Spray time sufficient 49 717 Automate spraying Mfg Engineering by 0X 12 15 Rejected due to complexity of different doors on the same line SAMPLE a2 c d e f g h i j k m ----n---- l h b 1a B D G A F C E H Table IV.1 Sample PFMEA Form with Minimal Information Elements & Example Entries
Chapter IV Process Failure Mode and Effects Analysis 109 Action Results (m-n) This section identifies the results of any completed actions and their effect on S, O, D rankings and RPN. Action(s) Taken and Completion Date (m) After the action has been implemented, enter a brief description of the action taken and actual completion date. Severity, Occurrence, Detection and RPN (n) After the preventive/corrective action has been completed, determine and record the resulting severity, occurrence, and detection rankings. Calculate and record the resulting action (risk) priority indicator (e.g., RPN). All revised rankings should be reviewed. Actions alone do not guarantee that the problem was solved (i.e., cause addressed), thus an appropriate analysis or test should be completed as verification. If further action is considered necessary, repeat the analysis. The focus should always be on continuous improvement.
Chapter IV Process Failure Mode and Effects Analysis 110 Process Step/Function Requirement Failure Mode Cause Prevention Controls Detection Controls Recommended Actions Visual aids illustrating correct quantity Four screws Fewer than four screws Too few screws inadvertently installed Operator training Visual Inspection in station In-station torque monitoring; Line lockout if fewer than four Visual aids illustrating correct screw Op. 20 (attach seat cushion to track using a torque gun) Select four screws Specified screws Wrong screw used (larger dia.) Similar screws available at station Operator training Visual inspection in station In-station torque angle monitoring; Line lockout if angle not met Error proof by design: use one type screw for station/product Visual aids identifying location of first screw Op. 20 (attach seat cushion to track using a torque gun) Beginning with right front hole, torque each screw to the required torque Assembly sequence: First screw in right front hole Screw placed in any other hole More than one hole available to operator Operator training Visual inspection in station Add position sensor to nut runner not allowing tool to operate unless runner is aligned with correct hole Table IV.5 Examples of Causes, Controls and Actions Maintaining PFMEAs The PFMEA is a living document and should be reviewed whenever there is a product or process design change and updated, as required. Another element of on-going maintenance of PFMEAs should include a periodic review. Specific focus should be given to Occurrence and Detection rankings. This is particularly important where there have been product or process changes or improvements in process controls. Additionally, in cases where either field issues or production issues, such as disruptions, have occurred, the rankings should be revised accordingly. Leveraging PFMEAs The use of a fundamentally sound PFMEA is the starting point that provides the greatest opportunity to leverage the use of past experience and knowledge.
Chapter IV Process Failure Mode and Effects Analysis 111 If a new project or application is functionally similar to the existing product and the process to be used is similar, a single PFMEA may be used with customer concurrence. If there are differences, the team should identify and focus on the effects of these differences. Linkages The PFMEA is not a “stand-alone” document. Figure IV.5 shows some common linkages. PFMEA DFMEA, Process Flow Diagram, etc. Process Control Plans Figure IV.5 PFMEA Information Interrelationship Flow To DFMEA In the development of a PFMEA it is important to utilize the information and knowledge gained in the creation of the DFMEA. However, the link between the two documents is not always obvious. The difficulty occurs because the focus of each FMEA is different. The DFMEA focuses on part function whereas the PFMEA focuses on the manufacturing steps or process. Information in the columns of each form is not directly aligned. For example, Item/Function-Design does not equal Process Functions/Requirements; potential design failure mode does not equal potential process failure mode; potential design cause of failure does not equal potential process cause of failure. However, by comparing the overall analysis of design and process, a connection can be made. One such connection is between the characteristics identified during the DFMEA and PFMEA analysis. Another connection is the relationship between potential design cause of failure (DFMEA) and potential process failure mode (PFMEA). For example, the design of a feature such as a hole can cause a particular failure mode. The corresponding process
Chapter IV Process Failure Mode and Effects Analysis 112 failure mode is the inability of the process to manufacture the same feature as designed. In this example, the potential design cause of failure (hole diameter designed too large) would appear to be similar to the potential process failure mode (hole drilled too large). The potential effect of the failure mode for both design and process may be identical if there were no additional process related effects. In other words, the end result (effect) of the failure mode is the same, but there are two distinct causes. While developing the PFMEA, it is the team’s responsibility to ensure that all process related potential failure modes which lead to product related effects are consistent between the DFMEA and the PFMEA. To Control Plan In addition to the list of Recommended Actions and their subsequent follow-up as a result of the PFMEA activity, a Control Plan should be developed13. Some organizations may elect not to specifically identify the related product and process characteristics” in the PFMEA. In this situation, the “Product Characteristics” portion of the Control Plan may be derived from the “Requirements” portion of the “Process Function/Requirements” column and the “Process Characteristics” portion may be derived from the “Potential Cause(s) of Failure Mode” column. When the team develops the Control Plan, they need to assure that the PFMEA current controls are consistent with the control methods specified in the Control Plan. 13 Guidelines for Control Plan development are included in Chrysler, Ford, GM; Advanced Product Quality Planning and Control Plan (APQP), AIAG.
113 APPENDICES
Appendix A Sample Forms 114 Appendix A: Sample Forms DFMEA Forms • Form A: Basic form (with minimal information)14 o With Prevention and Detection Controls as separate columns15 • Form B: Form with Item/Function and Requirements in separate columns o To assist in the determination of failure modes • Form C: Form A with Prevention Controls column to the left of the Occurrence column o To better show the relationship between prevention controls and occurrence ranking • Form D: Form B and C combined • Form E: Form D with separate columns for Current Detection Design Controls (Cause and Failure Mode) o To highlight the need to consider cause-related controls • Form F: Form B with separate columns for Responsibility and Target Completion Date and Actions Taken and Completion Date o To allow sorting by dates 14 This form was provided in the Chrysler, Ford, and GM; FMEA Manual 3rd Edition, AIAG. 15 Preventive and Detective Controls may be in the same column if each control is identified with a “P” or “D” respectively.
Appendix A Sample Forms 115 Potential Failure Mode Effect(s) of Potential Failure Severity ClassificationAction Results Actions Taken & Effective Date Responsibility & Target Completion Date Recommended Action Potential Cause(s) of Failure Prevention Detection RPN RPN Detection Detection Occurrence Occurance Severity Controls Controls Requirements POTENTIAL FAILUREMODEAND EFFECTSANALYSIS (DESIGN FMEA) FMEA Number Page of Prepared By: FMEA Date (Orig.) Design Responsibility ______________________________________ Key Date ________________________________________________ ______ System ______ Subsystem ______Component; _____________________________________ Model Core Team Current Design Current Design Item / FunctionYear(s)/Program(s)_________________________________ DFMEA Form A
Appendix A Sample Forms 116 DFMEA Form B
Appendix A Sample Forms 117 DFMEA Form C
Appendix A Sample Forms 118 DFMEA Form D
Appendix A Sample Forms 119 DFMEA Form E
Appendix A Sample Forms 120 DFMEA Form F
Appendix A Sample Forms 121 PFMEA Forms • Form A: Basic form (with minimal information)16 o With Prevention and Detection Controls as separate columns17 • Form B: Form A with Process Step/Function and Requirements as separate columns o To assist in the determination of failure modes • Form C: Form A with Prevention Controls Column to the left of the Occurrence column o To better show the relationship between prevention controls to occurrence ranking • Form D: Form B and C combined • Form E: Form D with separate columns for Current Detection Process Controls (Cause and Failure Mode) o To highlight the need to consider cause related controls • Form F: Form B with separate columns for Responsibility and Target Completion Date and Actions Taken and Completion Date o To allow sorting by dates • Form G: Form B with ID, Product and Process within a bridged Requirements column o To provide consistency among the Process Flow, PFMEA and Control Plan • Form H: Form D and G combined 16 This form was adapted from that provided in the Chrysler, Ford, and GM; FMEA Manual 3rd Edition, AIAG. 17 Preventive and Detective Controls may be in the same column if each control is identified with a “P” or “D” respectively.
Appendix A Sample Forms 122 Potential Failure Mode Effect(s) of Potential Failure Severity ClassificationAction Results Actions Taken & Effective Date Responsibility & Target Completion Date Recommended Action Potential Cause(s) of Failure RPN RPN Detection Detection Occurrence Occurance Severity Controls Controls Requirements POTENTIAL FAILUREMODEAND EFFECTSANALYSIS (PROCESSFMEA) FMEA Number Page of Prepared By: FMEA Date (Orig.) Process Responsibility ______________________________________ Key Date __________________________________________________ Item: _________________________________________________ Model Core Team Process Step Current Process Current Process / Function Year(s)/Program(s)_________________________________ PFMEA Form A
Appendix A Sample Forms 123 PFMEA Form B
Appendix A Sample Forms 124 PFMEA Form C
Appendix A Sample Forms 125 PFMEA Form D
Appendix A Sample Forms 126 Potential Failure Mode Effect(s) of Potential Failure Severity ClassificationAction Results Actions Taken & Effective Date Responsibility & Target Completion Date Recommended Action Potential Cause(s) of Failure Cause Failure Mode Prevention RPN RPN Detection Detection Occurrence Occurance Severity Controls Requirements POTENTIAL FAILUREMODEAND EFFECTSANALYSIS (PROCESSFMEA) FMEA Number Page of Prepared By: FMEA Date (Orig.) Process Responsibility ______________________________________ Key Date __________________________________________________ Item: _________________________________________________ Model Year(s)/Vehicle(s )__________________________________ Core Team Current Process Current Detection Process Controls Function Process Step PFMEA Form E
Appendix A Sample Forms 127 PFMEA Form F
Appendix A Sample Forms 128 PFMEA Form G
Appendix A Sample Forms 129 PFMEA Form H
Appendix B System Level FMEA 130 Appendix B: System Level FMEA The process for a System FMEA is generally the same as the development of other FMEAs. The major differences between System level FMEAs and other types of FMEAs is the focus on functions and relationships that are unique to the system as a whole (i.e., do not exist at lower levels). The System level FMEA includes failure modes associated with interfaces and interactions in addition to considering single point failures which is the primary focus of product level FMEAs. To help illustrate the meaning of System, Subsystem, and Component FMEAs, two examples have been constructed below in Figure B.1 (for Interfaces and Interactions) and in Figure B.2 (for Item, Function, and Failure Modes.). Figure B.1 Interfaces and Interactions The FMEA team is responsible for specifying the scope of its respective FMEAs. The example in Figure B.1 shows that the team has specified Subsystems A, B, C, and D along with the surrounding environment as comprising the System that must be considered while completing the System FMEA.
Appendix B System Level FMEA 131 Interfaces In Figure B.1, interfaces between subsystems are shown where Subsystem A touches and (connects with) Subsystem B, B touches or connects with C, and a clearance between D and B, signified by the dashed line. The Environment also touches each of the subsystems listed in Figure B.1, which requires the “Environmental Interfaces” be considered when completing the FMEA. Also, the interfaces to major and minor subsystems, whether direct or indirect, should be included. The interfaces which are identified in the System FMEA should be included in the respective Subsystem FMEA. Figure B.2 shows a system and its interrelationships in a “hardware” oriented approach. Interactions A change in one subsystem or component may cause a change in another subsystem or component. In Figure B.1, interactions between subsystems and components can occur among any of the interfacing systems. For example, Subsystem A heats up, resulting in Subsystem B and D gaining heat through their respective interfaces, as well as Subsystem A giving off heat to the environment. Interactions might also occur among ‘non-contacting’ systems via transfer through the ‘environment’. For example, if the environment is composed of high humidity and Subsystems A and C are dissimilar metals separated by a non-metal composing Subsystem B, Subsystem A and C can still have an electrolytic reaction due to the moisture from the environment. Thus, interactions among non-contacting subsystems can be relatively difficult to predict but are important and should be considered.
Appendix B System Level FMEA 132 Figure B.2 Item, Functions, and Failure
Appendix B System Level FMEA 133 Relationships Multiple Levels of Design FMEAs More likely than not, the focus of a DFMEA is an item which is a subset of a larger system. The FMEAs at the different levels of the design hierarchy (i.e., system, subsystem and component) are linked through the cause Æ failure mode Æ effect of failure relationships. This is a two way linkage (see Figure B.3): From Lower to Higher Level: The effect of a failure mode at a given level is a failure mode at the next higher level. For example, the effect of a part 2 failure mode would be a failure mode of module 3 either directly or indirectly by causing another part to fail. The effect of a module 4 failure mode is a failure mode of subsystem 4. Consequently, the effect of a failure mode at any sublevel may ultimately become a system failure mode with its customer / user related effects. From Higher to Lower level: The linkage from a higher level to the next lower level is related to the physics of failure rather than a pure cause and effect relationship since in the development of a DFMEA, the causes identified at any level deal with the design process and only indirectly with the failure mechanisms. Understanding these relationships will provide a consistency of analysis and an economy of effort in the development of DFMEAs.
Appendix B System Level FMEA 134 Figure B.3 DFMEA Effects Linkages
Appendix D Alternative Analysis Techniques 135 Appendix C: Alternative Risk Assessments Alternatives to RPN The risk priority number is the product of the severity (S), occurrence (O), and detection (D) rankings. (S) x (O) x (D) = RPN Within the scope of the individual FMEA, this value (between 1 and 1000) can be used to assist the team in ranking the concerns in the design of the product and process. The table below, however, illustrates how different Severity (S), Occurrence (O) & Detection (D) scenarios result in equal RPN values. 18 Upon review of each scenario, priorities would not be established by the team based on the RPN alone. Fifteen Different Situations with an RPN=360 Severity of Problem Likelihood of Occurrence Likelihood of Detection 1 Hazardous 10 High 9 Moderate 4 2 Hazardous 10 Moderate 6 Low 6 3 Hazardous 10 Moderate 4 Very Remote 9 4 Hazardous 9 Very High 10 Mod High 4 5 Hazardous 9 High 8 Moderate 5 6 Hazardous 9 Moderate 5 Remote 8 7 Hazardous 9 Moderate 4 Impossible 10 8 High 8 High 9 Moderate 5 9 High 8 Moderate 5 Very Remote 9 10 Moderate 6 Very High 10 Low 6 11 Moderate 6 Moderate 6 Impossible 10 12 Moderate 5 High 9 Remote 8 13 Moderate 5 High 8 Very Remote 9 14 Moderate 4 Very High 10 Very Remote 9 15 Moderate 4 High 9 Impossible 10 The ease of calculation and sorting of this index has led many to use it exclusively and without consideration to what may be a more appropriate means of prioritizing. Examples of some such alternatives follow. 18 Used with permission from Whirlpool Corporation, ©2005, 2006
Appendix D Alternative Analysis Techniques 136 Alternative: SO (S x O) Some organizations may choose to primarily focus on Severity and Occurrence. The SO index is the product of the Severity, and Occurrence rankings. In using this index, the organization may focus on how to reduce SO by reducing the value of “O” through preventive actions. Furthermore this may lead to subsequent detection improvements for those with the highest SO value. Alternative: SOD, SD Some organizations have chosen to use SOD or SD as a prioritization tool. SOD is the non-arithmetic combination of the Severity, Occurrence and Detection rankings. SD is the nonarithmetic combination of the Severity and Detection rankings. Example (SOD): Severity, S = 7 Occurrence, O = 3 Detection, D = 5 The resulting SOD is 735 Example (SD): Severity, S = 7 Detection, D = 5 The resulting SD is 75 The SOD, when sorted in numerical, descending order, will prioritize the scenarios first by severity, second by occurrence and lastly by detection. S O D RPN SOD SD 7 7 3 147 773 73 7 3 7 147 737 77 3 7 7 147 377 37 Table C.1 Contrast among RPN, SOD and SD Just as with RPN, use of the SOD/SD index should be used in context of team discussion. Defining priorities simply based on the SOD has limitations just as with the RPN. For example, a failure mode with a SOD of 711 would be ranked higher (i.e., have to be considered before) a failure mode with 599. Equal RPN Values Very Different Scenarios
Appendix D Alternative Analysis Techniques 137 Appendix D: Alternative Analyses Techniques Failure Mode and Effects Analysis is one of many techniques used to evaluate and analyze design risk. Other methods have been developed for specific areas and can be used to complement the analysis in the FMEA process. They may be used as a replacement for an FMEA with authorization by the customer. These are only a few of the examples. Failure Mode, Effect and Criticality Analysis (FMECA) FMECA is similar to FMEA. The C in FMECA indicates that the criticality (or severity) of the various failure effects are considered and ranked. Today, FMEA is often used as a synonym for FMECA. Design Review Based on Failure Modes (DRBFM) Design Review Based on Failure Modes is a cause and effect analysis of concerns related to a design change. It is a tool used to guide and manage good discussion in relation to the change. DRBFM focuses on the impact of the change on design, evaluation procedures, and manufacturing systems with the intent of anticipating and preventing problems. A design review by subject matter experts to evaluate the change(s) and related improvements is an integral part of DRBFM. (Reference Figure D.1). Fault Tree Analysis (FTA) FTA is a technique for system analysis where system faults are analyzed from a single potential failure to identify all possible causes. FTA considers combinations of interdependent as well as independent causes. In addition to the structure of the fault tree and all of the logic interdependencies, the FTA normally includes the failure probabilities identification. This allows the calculation of system reliability given the component reliabilities.19 (Reference Figure D.2). 19 References: IEC 61025; QICID (ASQ-20352).
Appendix D Alternative Analysis Techniques 138 Figure D.1 Example of DRBFM Elements
Appendix D Alternative Analysis Techniques 139 Figure D.2 FTA Tree Structure
References and Suggested Readings 140 References and Suggested Readings IEC 60300-3-1, Dependability management – Part 3-1: Application guide – Analysis techniques for dependability – Guide on methodology. IEC 60812, Edition 2; Failure modes and effects analysis, January 2006. IEC 61025, Edition 2; Fault tree analysis, January 2007. QICID (ASQ-20352) “System Reliability Through Fault Tree Analysis”. SAE ARP 5580, Recommended Failure Modes and Effects Analysis (FMEA). Practices for NonAutomotive Applications. (Replacement for MIL-STD-1629A, 1998 (withdrawn)). SAE J1739:2002, Potential Failure Mode and Effects Analysis in Design (Design FMEA) and Potential Failure Mode and Effects Analysis in Manufacturing and Assembly Processes (Process FMEA). Alfredo, H.S. Ang and Wilson, H. Tang (1990). “Probability Concepts in Engineering Planning and Design, Volume II -- Decision Risk and Reliability”, Wiley Publications. Bowles, J. (2003). “An Assessment of RPN Prioritization in a Failure Modes Effects and Criticality Analysis”, Proceedings Annual Reliability and Maintainability Symposium, pp 380-386; also in Journal of the IEST, Institute of Environmental Sciences and Technology, Vol 47, 2004, pp. 51-56. Krasich, M. (2007). “Physics of Failure Approach to FMEA”, Tutorial Proceedings Reliability and Maintainability Symposium. Krasich, M. (2005). “Fault Tree Analysis in Product Reliability Improvement”, Tutorial Proceedings Reliability and Maintainability Symposium. O’Conner, P.D.T., (2002). Practical Reliability Engineering. 4th edition, (Wiley). Shu-Ho Dai and Ming-O Wang (1992), Reliability Analysis in Engineering Applications, Van Nostrand Reinhold. Wheeler, D. J. (2005). The Six Sigma Practitioner's Guide to Data Analysis, SPC Press, Knoxville, pp.311- 315. Rausand, M. (2004). System Reliability Theory (2nd ed), Wiley, 2004.
Index 141 Index APQP (Advanced Product Quality Planning), 2, 5 block diagram, 18, 19, 29 classification, 39, 91 continuous improvement, 6, 57, 63, 103, 107, 109 control plans, 6, 13, 111 cross-functional, 2, 9, 17, 69, 71 current design controls, 49, 53 design improvements, 16 design intent, 11, 12, 22, 29, 41, 49, 68, 79 design life, 45 detection, 13, 18, 49, 51, 57-64, 68, 73, 95, 99- 110, 135, 136 detection controls, 49, 66, 99, 107 DFMEA (Design Failure Mode and Effects Analysis), 5, 16-19, 22, 25, 29, 39, 41, 64-66, 70, 73, 83, 84, 111, 133 DOE (Design of Experiments), 61, 107 DRBFM (Design Review by Failure Mode), 137, error proofing, 73, 105 evaluation criteria, 37, 45, 53, 87, 92, 99 flow diagram, 70, 71, 81, 107 FMECA (Failure Mode, Effect and Critical Analysis), 3, 137 Follow-up, 6 FTA (Fault Tree Analysis), 137, 139 function, 16, 18, 19 ,21 , 29 , 31, 35, 71, 79, 111 functional requirements, 8,16,18, 25 interactions, 3,10, 130, 131 interfaces, 10, 11, 29, 130,131 item, 73, 75, 111, 133 linkages, 65, 111, 134 mistake proofing, 61, 107 occurrence, 3, 13, 45, 46, 49, 53, 57, 59, 61, 63, 64, 68, 69, 92, 93, 95, 99, 103, 105, 107, 109, 110, 135, 136 OEM (GM, Ford, Chrysler), 11, 17, 27, 75 PFMEA (Process Failure Mode and Effects Analysis), 5, 17, 66, 68-71, 75, 77, 83, 91, 95, 110, 111 potential cause, 12, 39, 41, 91, 92 potential failure mode, 11, 16-18, 31, 61, 70-71, 81, 112 preventive controls, 45 process step, 77, 79, 107 recommended actions, 6, 13, 18, 57, 59, 61, 103, 107 responsible engineer, 17, 63, 69, 70, 91, 107 RPN (Risk Priority Number), 57, 59, 63, 103, 105, 109, 135, 136 scope, 3, 4, 8, 10, 11, 18, 25, 68, 70, 71, 73, 75, 130 SD (Ranking by Severity and Detection), 136 Severity, 13, 37, 57, 59, 63, 84, 87, 103, 109, 135, 136 SO (Ranking by Severity and Occurrence), 136 SOD (Ranking based on Severity, Occurrence and Detection), 136 SPC (Statistical Process Control), 95, 107 special characteristic, 39, 91 specification, 11, 13, 61, 107 team, 2, 4, 5, 8, 9, 10, 14, 17, 18, 21, 22, 27, 29, 35, 37, 41, 45, 49, 53, 57, 59, 69, 71, 73, 81, 87, 91, 95, 99, 103, 105, 111 team leader, 6, 9, 69, 70, 107 thresholds, 57, 59, 103, 105 validation, 16, 31, 49, 59, 61